Automatic resetting of control system for loss of functionality

Abstract

An electronic control system, as for instance a microcomputer in a microwave oven, is automatically reset when a signal, normally provided by the microcomputer within some normal interval relative to some reference, fails to occur. A reset command signal is generated and resets the microcomputer to some initial point from which normal operation may begin or resume and at which certain output loads may be rendered inoperative. A display device associated with the appliance is repetitively scanned at some normal interval and may provide the monitored signal. Circuitry capable of generating a reset-command signal is inhibited by the occurrence of a transition attending the display scan signal so long as it recurs within the particular interval. A timing capacitor is reset, as by being discharged, each time a transition attending a display scan signal occurs. If the capacitor is not reset, the voltage thereon ultimately attains a level which results in the generation of the reset command. Repetitive time-spaced reset commands may also be provided to insure success of the resetting operation. This reset command generating circuitry may be independent of and external to the microcomputer.

Having thus described a typical embodiment of our invention that which we claim as new and desire to secure by Letters Patent of the United States is: 
     
       1. In an appliance control system for controlling the operation of electrical control signal responsive means associated with an appliance, the control system including input means for entering functional electrical commands, electrical signal processing means connected to the control signal responsive means and receiving input commands from the input means, the signal processing means containing a programmed memory for storing instruction words which define operating sequences for the control signal responsive means, the signal processing means further including logic means for sequentially executing the instruction words to provide control signals to operate the control signal responsive means in response to commands from the input means, the signal processing means being programmed to provide at a location a signal having a voltage level transition normally occurring within a particular time interval relative to a certain reference, and the signal processing means also including means responsive to a reset command extended thereto for setting the execution of the programmed instruction words to a predetermined initial point in the program sequence from which a predetermined sequence of initializing operations is automatically initiated, the improvement comprising: means automatically responsive to said normally occurring signal transition failing to occur at said location within said particular time interval relative to said reference for generating a reset command signal and extending said reset command signal to said means for setting the execution of the programmed instruction words to said initial point, said reset command generating means comprising a timing capacitance means and threshold means for determining said particular time interval, said capacitance means being charged at a predetermined rate and being connected to said threshold means for providing a said reset command signal when said threshold is exceeded, and means responsive to said normally-occurring signal transition for discharging said timing capacitance means, said normally-occurring signal transition recurring at shorter intervals than the interval for said timing capacitance means to charge to said threshold.   
     
     
       2. The control system of claim 1 wherein at least one of said control signal responsive means comprises display means, said display means normally being repetitively scanned by a display scan signal normally recurring at predetermined fixed intervals, said display scan signal being said normally occurring signal. 
     
     
       3. The control system of claim 2 wherein said control signal responsive means additionally comprises at least one means for actively controlling operation of the appliance, said at least one active means having active and inactive functional states, and said at least one active means being placed in said inactive state by said initializing operations initiated when said program sequence is set at said predetermined initial point. 
     
     
       4. A control system of claim 3 wherein said appliance is a microwave oven and said at least one active means comprises a source of cooking energy. 
     
     
       5. The control system of claim 1 wherein said signal processing means comprises an integrally-formed microcomputer having input and output ports and a reset port, at least some of said output ports being connected with said control signal responsive means to extend said control signals thereto and at least some of said input ports receiving input commands from said input means, said location at which said normally occurring signal transition appears is accessible externally of said microcomputer and said reset command generating means is located externally of and is connected to said microcomputer. 
     
     
       6. The control system of claim 5 wherein said means for setting the execution of the programmed instruction words to said initial point is responsive to a transition in the level of the reset command extended thereto and further including gating means for controllably extending said reset command signal to said means for setting the execution of the programmed instruction words to said initial point, said gating means having applied thereto a periodic signal having a repetition rate which is directly proportional to the frequency of and is derived from the available AC line power, said gating means serving to pass said reset command signal only periodically as determined by said periodic signal and the duty cycle of said periodic signal being of such duration that at least a minimum delay exists between successive reset command signals passed by the gating means whereby restoration of operation of said signal processing means may occur. 
     
     
       7. The control system of claim 6 wherein said memory is a fixed, permanently programmed read-only-memory. 
     
     
       8. The control system of claim 1 wherein said means for setting the execution of the programmed instruction words to said initial point is responsive to a transition in the level of the reset command extended thereto and further including gating means for controllably extending said reset command signal to said means for setting the execution of the programmed instruction words to said initial point, said gating means having applied thereto a periodic signal having a repetition rate which is directly proportional to the frequency of and is derived from the available AC line power, said gating means serving to pass said reset command signal only periodically as determined by said periodic signal and the duty cycle of said periodic signal being of such duration that at least a minimum delay exists between successive reset command signals passed by the gating means whereby restoration of operation of said signal processing means may occur. 
     
     
       9. In an appliance control system for controlling the operation of electrical control signal responsive means associated with an appliance, the control system including input means for entering functional electrical commands, electrical signal processing means connected to the control signal responsive means and receiving input commands from the input means, the signal processing means containing a programmed memory for storing instruction words which define operating sequences for the control signal responsive means, the signal processing means further including logic means for sequentially executing the instruction words to provide control signals to operate the control signal responsive means in response to commands from the input means, the signal processing means being programmed to provide at a location a signal having a voltage level transition normally occurring within a particular time interval relative to a certain reference, and the signal processing means also including means responsive to a transition in the level of a reset command extended thereto for setting the execution of the programmed instruction words to a predetermined initial point in the program sequence from which a predetermined sequence of initializing operations is automatically initiated, the improvement comprising: means automatically responsive to said normally occurring signal transition failing to occur at said location within said particular time interval relative to said reference for generating a reset command signal and gating means for controllably extending said reset command signal to said means for setting the execution of the programmed instruction words to said initial point, said gating means having applied thereto a periodic signal having a repetition rate which is directly proportional to the frequency of and is derived from the available AC line power, said gating means serving to pass said reset command signal only periodically as determined by said periodic signal and the duty cycle of said periodic signal being of such duration that at least a minimum delay exists between successive reset command signals passed by the gating means whereby restoration of operation of said signal processing means may occur.